In recent years, a technology called OpenFlow has been proposed (refer to Non-Patent Literatures 1 and 2). OpenFlow treats communication as an end-to-end flow and performs path control, failure recovery, load balancing, and optimization for each flow. An OpenFlow switch, specified in Non-Patent Literature 2, comprises a secure channel for communicating with an OpenFlow controller and operates according to a flow table, an addition to or rewriting of which is suitably instructed by the OpenFlow controller. In the flow table, a set of matching rule (Match Fields) to be matched against a packet header, flow statistics (Counters), and Instructions defining the processing contents is defined for each flow (refer to the section of “4.1 Flow Table” in Non-Patent Literature 2).
For instance, upon receiving a packet, the OpenFlow switch searches for an entry having a matching rule (refer to “4.3 Match Fields” in Non-Patent Literature 2) that matches the header information of the received packet in the flow table. When an entry matching the received packet is found as a result of the search, the OpenFlow switch updates the flow statistics (Counters) and performs the processing contents (packet transmission from a designated port, flooding, discard, etc.) written in the instruction field of the entry on the received packet. On the other hand, when no entry matching the received packet is found as a result of the search, the OpenFlow switch requests the OpenFlow controller to set an entry via the secure channel, transmitting a request (Packet-In message) for control information for processing the received packet. The OpenFlow switch receives a flow entry that defines the processing contents and updates the flow table. As described, the OpenFlow switch forwards packets using entries stored in the flow table as control information.
[Non-Patent Literature 1]
    Nick McKeown, et. al. “OpenFlow: Enabling Innovation in Campus Networks,” [online], [searched on Nov. 27, 2012], the Internet <URL: http://www.openflow.org/documents/openflow-wp-latest.pdf>[Non-Patent Literature 2]    “OpenFlow Switch Specification” Version 1.1.0 Implemented (Wire Protocol 0x02), [online], [searched on Nov. 27, 2012], the Internet <URL:http://www.openflow.org/documents/openflow-spec-v1.1.0.pdf>